Japanese deer fern, Blechnum nipponicum

Japan’s moist woods are home to a small growing Blechnum species, B. nipponicum, that may either be distinct, or a variety of the much more far ranging species, B. spicant, the deer fern. Regardless, this one is special in my mind, a perfect looking fern, worthy of any serious gardener’s eye.

Blechnum nipponicum is a small evergreen fern with two distinct frond types, fertile and sterile. Both are once pinnate and uncomplicated looking. The sterile fronds are more showy with broader pinnae, and are up to 8-30 cm long and 3-8 cm wide. The pinnae are simple, flat, and oblong. They extend nearly from the base of each stipe to the very tip of the frond in opposing rows presented in a flat plain, and are longer at the center of the frond. The sterile fronds grow in a lovely rosette and usually have an elegant arch to them. They stay close to the ground rather than growing vertically.

Once mature, the rosette of sterile fronds turn a gorgeous brilliant green. The Japanese name, Shishigashira, meaning "lion's mane" is perhaps a reference to its outward appearance - a lion's head!

The fertile fronds grow vertically, are much taller, and have much more narrow pinnae. They also are born in opposite pairs, but are highly reduced towards the stipe end, and grow much looser on the blade as well. The indusia and accompanying sori are long and linear, originating at the base of each pinna and extending nearly the entire length of it. They occur in pairs on either side of the costa. The croziers start out bright electric green to deep red and the new fronds often have this same color for some time. These eventually grow progressively darker green, a common trait in many ferns, especially Blechnum species.

The erect fertile fronds of Blechnum nipponicum expand a bit later than the sterile ones, and flush a deeper red color. Whether is species is distinct or falls within Blechnum spicant is still in question. It is a relatively small form regardless.

It occurs in small colonies or as individual plants in any moist forest in deep to light shade, but sometimes can be seen on sunny roadsides in thick growth with grasses and small shrubs. Like many other types of fern, it readily colonizes raw earth in cuts created by roads, paths, and landslides as well. Found from near sea-level to 1000+ m, but most common in lower elevations, 200-400 m.

This species is apparently widespread on the mainland islands of Japan. I’m unsure of its presence on the islands south of Yaku Island (where it is represented by a dwarf race, or so I’ve heard), or in neighboring Asian countries. This plant is also treated as a variety of the circumboreal species B. spicant, with which it is obviously very closely allied, commonly called deer fern. Given that fern’s incredible range, extending from England throughout much of Europe to the Caucus Mountains, north Africa, northeast Asia, and western North America, it is not surprising that various forms have evolved. Whether this plant falls into B. spicant or is distinct is still in question.

This delightful fern is thankfully very common and readily grows in and around the works of humans. In particular it seems to favor cuts in hillsides created by roads and trails, and it isn’t put off by plantation forests either. It is a small fern generally, not more than 30 cm tall, but the fertile fronds can occasionally grow 45 cm or higher, and the span of the sterile fronds can exceed 35 cm as well. One of its more remarkable qualities is the brilliant hot pink/electric green colors of the newly growing fronds. It is truly amazing to see these in person on a spring day.

This electric show fades to a brilliant emerald green by June and by fall the fronds get an even deeper green. It isn’t uncommon to see a huge colony of these plants on a steep bank, or just one lone specimen on the leafy forest floor. The hairy, thick rhizome typically is at or just below the soil line, but sometimes erosion will expose it and the result is a tiny “trunked” plant. These “trunks” can sometimes be several centimeters in height, however this condition is unusual and not the typical habit of this species. Though common, this is one of my favorite Japanese ferns.

Japanese people love wild plants and relish growing many in their gardens, but for some reason this plant is never seen in gardens here. I’m not sure why, but it may be due to the difficulty of getting them going once moved. They seem to detest being moved to a new locale, no matter how carefully this has been done. To date I have transplanted a dozen or so, and none of them are really thriving despite efforts to give them good conditions. Based on naturally growing specimens, this species needs continuously moist, yet well draining soil. Any reasonable woods loam should do as long as the soil reaction is acidic. They seem quite tolerant of bright light and even a little sun, but very shady conditions seem just as good for them.

A rosette of newly grown fronds of Blechnum nipponicum are startling on a spring day. Wow, what a fern!

They can withstand temperatures to at least -10C (14 F) and probably much lower in the winter, and 35 C (95 F) or more in the summer. Given this broad range of conditions you would think it would be easy in cultivation, but it is not. Of my original transplants, a few are finally acting like they are settling in. They should be cold hardy to USDA zone 7 (probably colder with protection), and require a distinct cool down in winter. In the eastern USA zones 9a to 7 should be fine without protection. Without a doubt, this species is a temperate fern that strays into the subtropics, but is not subtropical by nature. This species is far more heat tolerant that B. spicant.

If you can get this one to establish, it is a lovely addition to the woodland garden. I would grow them for brilliant new fronds in and of themselves. It is not an easy species, but worthy of space in any suitable garden.

The sori of Blechnum nipponicum are in perfectly straight pairs on either side of the costa of each pinnae.